Before he was a presidential candidate, Donald Trump seemed to be in the camp of those who believed Congress was entitled to sign off before President Barack Obama launched a military strike in response to Syria’s use of chemical weapons.

“What will we get for bombing Syria besides more debt and a possible long term conflict? Obama needs Congressional approval,” Trump tweeted in August 2013.

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Now that he’s commander in chief, though, Trump says he had the legal authority to launch 59 cruise missiles at a Syrian government-held air base this week in the wake of a chemical gas attack on civilians.

“As Commander in Chief, the President has the power under Article II of the Constitution to use this sort of military force overseas to defend important U.S. national interests,” the White House statement read. “The United States has a strong national interest in preserving regional stability, averting a worsening of the humanitarian catastrophe in Syria, and deterring the use and proliferation of chemical weapons, especially in a region rife with international terrorist groups with long-standing interests in obtaining these weapons and using them to attack the United States and its allies and partners.”

White House officials said Friday that the legal basis for the Syria strikes was “very similar” to that for President Barack Obama’s intervention in Libya in 2011. That action was blessed by the Justice Department’s Office of Legal Counsel in a 14-page opinion that concluded the broader operation Obama ordered was still too small to amount to the kind of war-making that required congressional sign-off.

“The historical practice of presidential military action without congressional approval precludes any suggestion that Congress’s authority to declare war covers every military engagement, however limited, that the President initiates,” Justice Department official Caroline Krass wrote. “We believe applicable historical precedents demonstrate that the limited military operations the President anticipated directing were not a ‘war’ for constitutional purposes.”

Critics contend that opinion was off the mark and that the kind of military action a president can take without congressional approval is limited to small-scale raids.

“I’d consider ‘small’ a commando action like the one used to seize [Benghazi attack suspect Ahmed] Abu Khatallah in Libya, not a Tomahawk missile, and certainly not 59 of them,” said Notre Dame law professor Mary Ellen O’Connell.

O’Connell also rejected the Trump team’s comparison to the scenario that played out in Libya about six years ago.

“Libya had a [U.N.] Security Council authorization and this doesn’t, so this is another blow by the Trump administration against international institutions and international law,” the professor said. “They chose wisely because nobody wants to be saying anything that sounds soft about Assad or soft on the use of chemical weapons.”

Speaking to reporters Thursday night at Trump’s private club in Florida, Secretary of State Rex Tillerson seemed to be eager to rebut or pre-empt arguments that the operation violated international law. At the same time, he never quite conceded that was a concern and he appeared to choose his words carefully, calling the strikes “appropriate” but never explicitly defending their legality.

“It’s important that some action be taken on behalf of the international community to make clear that the use of chemical weapons continues to be a violation of international norms,” Tillerson said. “One of the existential threats we see on the ground in Syria is, if there are weapons of this nature available in Syria, the ability to secure those weapons and not have them fall into the hands of those who would bring those weapons to our shores to harm American citizens. ... We feel the strike itself was proportional because it was targeted at the facility that delivered this most recent chemical weapons attack. And in carrying this out, we coordinated very carefully with our international partners in terms of communicating with them around the world.”

O’Connell said Tillerson’s comments were a jumble of words used in international law discussions, but didn’t amount to a coherent argument.

“They put a few legal terms in there, that’s true, but they’re missing the phrase that pays, which is: What is the exception in the U.N. Charter that permits them to resort to force in the first place?” she said. “The irony is they’re saying, ‘Hey, we’re citing the Chemical Weapons Convention as an important international war norm, without in any way offering an explanation of how they get to violate an equally important norm which is the prohibition on aggression. ... It doesn’t work that way.”

What’s less clear is what consequences Trump or the U.S. will face for the strikes. Critics say the alleged failure to abide by international law in the Syria case could undercut U.S. efforts to pressure other countries over their aggressive acts, such as Russia’s invasion of Crimea or China’s assertive moves in the South China Sea.

“If we maintain a consistent, compliant position with the U.N. charter, we’re in a much better position to make the case against those countries,” O’Connell said.

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One attorney who has filed suits to try to assert congressional control over military operations said he is troubled that while the White House officials and Republican lawmakers are praising just-confirmed Supreme Court nominee Neal Gorsuch for his “originalist” approach to the Constitution, they’re ignoring what the founding document says about which branch of government has the power to make war.

“As usual, the textualists and originalists are AWOL about the use of the war power in the wake of a hearing where that was a rallying point of supporters of Justice Gorsuch,” said George Washington University law professor Jonathan Turley. “The situation is quite alarming. ... I think the framers would’ve been horrified by the notion that war would become discretionary and unilateral to the president.”

Former George W. Bush National Security Council and State Department legal adviser John Bellinger said arguments that Trump lacks authority for the strike under U.S. law are relatively weak.

“I think most Bush and Obama lawyers, and probably Obama himself, would say he doesn’t need congressional approval to do this, even if it may be a good idea to get it,” Bellinger said.

However, Bellinger said the international law basis for Trump’s Syria strikes is highly controversial and far from clear cut. And some Trump officials may not care.

“That’s my worry. … We had this in Bush administration in the Iraq War,” Bellinger said. “I get the sense there are a number of people in the Trump administration who don’t really believe there is a need for international legitimacy. The reason for that is not just to sort of soothe the ruffled feathers of other countries, but so we can criticize other countries when they don’t act consistent with the law, like the Russians, the Chinese and the Iranians. This is about reciprocity, not just the State Department wanting to be liked.”

CORRECTION: An earlier version of this story misidentified Krass as the current general counsel of the CIA. She left that post at the end of the Obama administration.